'Add documentation' link now changes to 'Edit documentation' as soon as qqq exists

The code which changes the text of the link has been moved to
ext.translate.editor.js and a deferred object has been created
in the ext.translate.helper.js.

Bug: 50954
Change-Id: I3c3e370c0320b6981c19b3f8684a1964d5451b8c
Merge "'Add documentation' link now changes to 'Edit documentation' as soon as qqq exists"